Then he had a brainstorm: it could be one of the cells that's gone bad, not the whole battery. Scoodidabop has some experience as an electrician, so he figured he could test it and replace any bad cells for about $45 apiece. He removed the battery unit from the trunk and over the course of two hours tested all 68 cells four times. He found nothing wrong. So he devised another type of test and checked every cell again. He couldn't find a problem with any of them.
Turns out the problem wasn't in the cells, but with the dirty and corroded copper connectors at the ends of the high-voltage cables. He pulled the 34 connectors and their steel nuts, soaked them in vinegar, gave them a light steel wool scrub, soaked them in baking soda and water to counteract the vinegar, applied an anticorrosive and reinstalled them. That took an hour. When he replaced the battery, the warning lights had all gone out and the battery worked perfectly. Skill level: experience. Cost: less than $10. Perhaps it's time for hybrids to be able to test their own cells individually. Dealers, too.